Forest operations,tree species composition and decline in rainfall explain runoff changes in the Nacimiento experimental catchments,south central Chile     

Andrés Iroumé  Julia Jones  James C. Bathurst 《水文研究》2021,35(6):e14257

Few long-term studies have explored how intensively managed short rotation forest plantations interact with climate variability. We examine how prolonged severe drought and forest operations affect runoff in 11 experimental catchments on private corporate forest land near Nacimiento in south central Chile over the period 2008–2019. The catchments (7.7–414 ha) contain forest plantations of exotic fast-growing species (Pinus radiata, Eucalyptus spp.) at various stages of growth in a Mediterranean climate (mean long-term annual rainfall = 1381 mm). Since 2010, a drought, unprecedented in recent history, has reduced rainfall at Nacimiento by 20%, relative to the long-term mean. Pre-drought runoff ratios were <0.2 under 8-year-old Eucalyptus; >0.4 under 21-year-old Radiata pine and >0.8 where herbicide treatments had controlled vegetation for 2 years in 38% of the catchment area. Early in the study period, clearcutting of Radiata pine (85%–95% of catchment area) increased streamflow by 150 mm as compared with the year before harvest, while clearcutting and partial cuts of Eucalyptus did not increase streamflow. During 2008–2019, the combination of emerging drought and forestry treatments (replanting with Eucalyptus after clearcutting of Radiata pine and Eucalyptus) reduced streamflow by 400–500 mm, and regeneration of previously herbicide-treated vegetation combined with growth of Eucalyptus plantations reduced streamflow by 1125 mm (87% of mean annual precipitation 2010–2019). These results from one of the most comprehensive forest catchment studies in the world on private industrial forest land indicate that multiple decades of forest management have reduced deep soil moisture reservoirs. This effect has been exacerbated by drought and conversion from Radiata pine to Eucalyptus, apparently largely eliminating subsurface supply to streamflow. The findings reveal tradeoffs between wood production and water supply, provide lessons for adapting forest management to the projected future drier climate in Chile, and underscore the need for continued experimental work in managed forest plantations.  相似文献   

关于改进的Encke方法中参考轨道的选择和校正     

刘林  胡松杰 《天文学报》1996,37(3):285-293

对于改进的Ｅｎｃｋｅ方法，选择适当的参考轨道是一个关键．然而，对于人造地球卫星长弧轨道计算，目前所给出的几种参考轨道均需要逐段校正，这将给定轨问题带来附加的复杂性．本文将仔细探讨如何选择参考轨道和减少校正次数．  相似文献   

八庙—青山金红石矿床化学成分与成矿关系     

徐少康  李博昀  程建祖  刘振山 《河南国土资源》1996,(4)

本矿床是我国金红石矿床重要的成因及工业类型，为具有特定化学成分的岩石在特定变质条件下形成的。本文通过对大量数据的处理，查明了化学成分与成矿的关系：高Ａｌ２Ｏ３、ＭｇＯ、Ｆｅ２Ｏ３＋ＦｅＯ、Ｋ２Ｏ、Ｐ２Ｏ５、Ｈ２Ｏ＋、ＭｎＯ，低ＳｉＯ２、ＣａＯ、Ｎａ２Ｏ、ＣＯ２、Ｓ等，利于钛富集；高ＴｉＯ２、ＭｇＯ、Ｐ２Ｏ５、Ｓ，低ＳｉＯ２、ＣａＯ、Ｋ２Ｏ、Ａｌ２Ｏ３、Ｆｅ２Ｏ３／ＦｅＯ，利于金红石形成；高Ｓｃ、Ｚｒ、Ｎｉ、Ｚｎ及Ｌａ／Ｙｂ，低Ｙ、Ｎｂ、Ｔｈ、Ｃｄ、Ｂａ、Ｂｅ、ΣＲＥＥ，利于金红石纯度提高。对研究矿床成因及寻找新的同类矿床等有重要意义  相似文献   

宁夏香山-天景山弧形断裂带新活动特征及1709年中卫南71/2级地震形变带   总被引：5，自引：1，他引：4       下载免费PDF全文

张维岐  焦德成  柴炽章  宋方敏  汪一鹏 《地震地质》1988,10(3):12

本文根据野外地质填图和水系位移测量结果,论述了香山-天景山弧形断裂带新生代有两个不同活动性质的阶段,即早期阶段的强烈挤压和晚期阶段的左旋走滑兼挤压。分析、讨论了不同活动阶段的时间界限和转变原因。指出了1709年中卫南71/_2级地震形变带的表现形式、延伸范围  相似文献   

The double solid reactant method: II. An application to the shallow groundwaters of the Porto Plain,Vulcano Island (Italy)     

Matteo Lelli  Roberto Cioni  Luigi Marini 《Environmental Geology》2008,56(1):139-158

This paper presents an example of application of the double solid reactant method (DSRM) of Accornero and Marini (Environmental Geology, 2007a), an effective way for modeling the fate of several dissolved trace elements during water–rock interaction. The EQ3/6 software package was used for simulating the irreversible water–rock mass transfer accompanying the generation of the groundwaters of the Porto Plain shallow aquifer, starting from a degassed diluted crateric steam condensate. Reaction path modeling was performed in reaction progress mode and under closed-system conditions. The simulations assumed: (1) bulk dissolution (i.e., without any constraint on the kinetics of dissolution/precipitation reactions) of a single solid phase, a leucite-latitic glass, and (2) precipitation of amorphous silica, barite, alunite, jarosite, anhydrite, kaolinite, a solid mixture of smectites, fluorite, a solid mixture of hydroxides, illite-K, a solid mixture of saponites, a solid mixture of trigonal carbonates and a solid mixture of orthorhombic carbonates. Analytical concentrations of major chemical elements and several trace elements (Cr, Mn, Fe, Ni, Cu, Zn, As, Sr and Ba) in groundwaters were satisfactorily reproduced. In addition to these simulations, similar runs for a rhyolite, a latite and a trachyte permitted to calculate major oxide contents for the authigenic paragenesis which are comparable, to a first approximation, with the corresponding data measured for local altered rocks belonging to the silicic, advanced argillic and intermediate argillic alteration facies. The important role played by both the solid mixture of trigonal carbonates as sequestrator of Mn, Zn, Cu and Ni and the solid mixture of orthorhombic carbonates as scavenger of Sr and Ba is emphasized.

Luigi Marini (Corresponding author)Email:

  相似文献   

Experimental constraints on the effects of pressure and H2O on the fractional crystallization of high-Mg island arc basalt     

Morihisa Hamada  Toshitsugu Fujii 《Contributions to Mineralogy and Petrology》2008,155(6):767-790

H₂O-undersaturated melting experiments of synthesized basalt (SiO₂ = 50.7 wt.%, MgO = 8.3 wt.%, Mg# = 60) were conducted at fO₂ corresponding to NNO+1 and NNO−1 to clarify the effects of pressure (2–7 kbar) and H₂O on fractional crystallization in island arcs. H₂O content was ranged from nominally anhydrous to 4.4 wt.%. Differentiation trends, namely the liquid lines of descent, change sensitively according to pressure-H₂O relations. Tholeiitic differentiation trends are reproduced with H₂O ≤ ∼2 wt.% in primary magma. With such quantities of H₂O, fractional crystallization is controlled by olivine + plagioclase at 2 kbar. Increasing the pressure from 2 to ≥4 kbar induces early crystallization of orthopyroxene instead of olivine and therefore SiO₂ enrichment in the residual melts is suppressed. Increasing H₂O (≥ ∼2 wt.% in primary magma) stabilizes clinopyroxene relative to orthopyroxene and/or magnetite. Although the phase relations and proportions strongly depend on fO₂ and H₂O content, differentiation trends are always calc-alkaline.  相似文献   

Water and power in Santiago de Chile: Socio-spatial segregation through network integration     

Géraldine Pflieger  Sarah Matthieussent 《Geoforum》2008,39(6):1907-1921

The analysis of the history of the management and distribution of electricity, water and sanitation networks in Santiago de Chile throws light on a problem which is central to thinking on the relationship between urban services management and territorial splintering: what is the impact of urban policy, in particular housing policy and urban planning, on access to services and on the potential levels of social segregation and institutional splintering of metropolises?The Chilean example is eminently anchored in its political and institutional history. We shall see, for example, that the authoritarian urban policy of the military government, associated with early liberal reform, enabled the improvement of access to networks in every municipality of the Greater Santiago area. However, this success, leading to the integration by urban services of a large territory, does not signify that networks remained neutral as regards the process of spatial segregation. Inversely, we can defend the theory that the presence of an integrated service was a necessary condition and a reinforcing factor of the process of urban spread and residential segregation. This paradoxical argument is a result of the ambivalent liberal network and urban policies of the military government. Urban expansion was largely sustained by the development of integrated infrastructures and universal services. The processes of liberalising land and urban services were mutually sustaining and provided the necessary conditions for the birth of an extremely intense movement of urban sprawl and segregation between 1985 and 2000.  相似文献   

Depths of Partial Crystallization of H2O-bearing MORB: Phase Equilibria Simulations of Basalts at the MAR near Ascension Island (7 11{degrees}S)     

Almeev  Renat; Holtz  Francois; Koepke  Jurgen; Haase  Karsten; Devey  Colin 《Journal of Petrology》2008,49(1):25-45

Phase equilibria simulations were performed on naturally quenchedbasaltic glasses to determine crystallization conditions priorto eruption of magmas at the Mid-Atlantic Ridge (MAR) east ofAscension Island (7–11°S). The results indicate thatmid-ocean ridge basalt (MORB) magmas beneath different segmentsof the MAR have crystallized over a wide range of pressures(100–900 MPa). However, each segment seems to have a specificcrystallization history. Nearly isobaric crystallization conditions(100–300 MPa) were obtained for the geochemically enrichedMORB magmas of the central segments, whereas normal (N)-MORBmagmas of the bounding segments are characterized by polybariccrystallization conditions (200–900 MPa). In addition,our results demonstrate close to anhydrous crystallization conditionsof N-MORBs, whereas geochemically enriched MORBs were successfullymodeled in the presence of 0·4–1 wt% H₂O in theparental melts. These estimates are in agreement with direct(Fourier transform IR) measurements of H₂O abundances in basalticglasses and melt inclusions for selected samples. Water contentsdetermined in the parental melts are in the range 0·04–0·09and 0·30–0·55 wt% H₂O for depleted and enrichedMORBs, respectively. Our results are in general agreement (within±200 MPa) with previous approaches used to evaluate pressureestimates in MORB. However, the determination of pre-eruptiveconditions of MORBs, including temperature and water contentin addition to pressure, requires the improvement of magma crystallizationmodels to simulate liquid lines of descent in the presence ofsmall amounts of water. KEY WORDS: MORB; Mid-Atlantic Ridge; depth of crystallization; water abundances; phase equilibria calculations; cotectic crystallization; pressure estimates; polybaric fractionation  相似文献   

Lithospheric Origin of Oligocene-Miocene Magmatism in Central Chile: U-Pb Ages and Sr-Pb-Hf Isotope Composition of Minerals     

Montecinos  P.; Scharer  U.; Vergara  M.; Aguirre  L. 《Journal of Petrology》2008,49(3):555-580

Establishing the petrogenesis of volcanic and plutonic rocksis a key issue in unraveling the evolution of distinct subduction-relatedtectonic phases occurring along the South American margin. Thisis particularly true for Cenozoic times when large volumes ofmagma were produced in the Andean belt. In this study we havefocused on Oligo-Miocene magmatism in central Chile at 33°S.Our data include field and petrographic observations, whole-rockmajor and trace element analyses, U–Pb zircon dating,and Pb, Sr, and Hf isotope analyses of plagioclase, clinopyroxene,and zircon mineral separates. Combined with earlier dating resultsthe new zircon ages define a 28·8–5·2 Maperiod of plutonic and volcanic activity that ceased as a consequenceof flattening subduction of the Nazca–Farallon plate.Rare earth elements patterns are variable, with up to 92 timeschondrite concentrations for light rare earth elements yielding(La/Yb)_N between 3·6 and 7·0, and an absence ofEu anomalies. Initial Pb isotope signatures are in the rangeof 18·358–19·023 for ²⁰⁶Pb/ ²⁰⁴Pb, 15·567–15·700for ²⁰⁷Pb/ ²⁰⁴Pb and 38·249–39·084 for ²⁰⁸Pb/²⁰⁴Pb. Initial ⁸⁷Sr/ ⁸⁶Sr are mostly in the range of 0·70369–0·70505,with two more radiogenic values at 0·7066. Initial Hfisotopic compositions of zircons yield exclusively positiveHf_i ranging between + 6·9 and + 9·6. The newlydetermined initial isotope characteristics of the Oligo-Miocenemagmas suggest that the mantle source lithologies are differentfrom both those of Pacific mid-ocean ridge basalt and oceanisland basalt, plotting in the field of reference values forsubcontinental lithospheric mantle, characterized by moderatelarge ion lithophile element–high field strengh elementdepletion and high ²³⁸U/ ²⁰⁴Pb. A Hf model age of 2 Ga is estimatedfor the formation of the subcontinental mantle–continentalcrust assemblage in the region, suggesting that the initialSr and Pb isotope ratios inferred for the source of the Oligo-Mioceneparental magmas are the result of later Rb and U enrichmentcaused by mantle metasomatism. A time-integrated model Rb/Srof 0·039 and µ 16 are estimated for the sourceof the parental magmas, consistent with ratios measured in peridotitexenoliths from continental areas. Evolution from predominant(>90%) basaltic–gabbroic to andesitic–dioriticmagmas seems to involve a combination of (1) original traceelement differences in the metasomatized subcontinental mantle,(2) different degrees of partial melting and (3) fractionalcrystallization in the garnet- and spinel-peridotite stabilityfields. The genesis of more differentiated magmas reaching rhyolitic–graniticcompositions most probably also includes additional crystalfractionation at both shallow mantle depths and within the crust,possibly leading to some very minor assimilation of crustalmaterial. KEY WORDS: calc-alkaline magmatism; Oligo-Miocene; U–Pb dating; Sr–Pb–Hf isotopes; central Chile  相似文献   

Phase Relations and Melting of Anhydrous K-bearing Eclogite from 1200 to 1600{degrees}C and 3 to 5 GPa     

Spandler  Carl; Yaxley  Greg; Green  David H.; Rosenthal  Anja 《Journal of Petrology》2008,49(4):771-795

To investigate eclogite melting under mantle conditions, wehave performed a series of piston-cylinder experiments usinga homogeneous synthetic starting material (GA2) that is representativeof altered mid-ocean ridge basalt. Experiments were conductedat pressures of 3·0, 4·0 and 5·0 GPa andover a temperature range of 1200–1600°C. The subsolidusmineralogy of GA2 consists of garnet and clinopyroxene withminor quartz–coesite, rutile and feldspar. Solidus temperaturesare located at 1230°C at 3·0 GPa and 1300°C at5·0 GPa, giving a steep solidus slope of 30–40°C/GPa.Melting intervals are in excess of 200°C and increase withpressure up to 5·0 GPa. At 3·0 GPa feldspar, rutileand quartz are residual phases up to 40°C above the solidus,whereas at higher pressures feldspar and rutile are rapidlymelted out above the solidus. Garnet and clinopyroxene are theonly residual phases once melt fractions exceed 20% and garnetis the sole liquidus phase over the investigated pressure range.With increasing melt fraction garnet and clinopyroxene becomeprogressively more Mg-rich, whereas coexisting melts vary fromK-rich dacites at low degrees of melting to basaltic andesitesat high melt fractions. Increasing pressure tends to increasethe jadeite and Ca-eskolaite components in clinopyroxene andenhance the modal proportion of garnet at low melt fractions,which effects a marked reduction in the Al₂O₃ and Na₂O contentof the melt with pressure. In contrast, the TiO₂ and K₂O contentsof the low-degree melts increase with increasing pressure; thusNa₂O and K₂O behave in a contrasted manner as a function ofpressure. Altered oceanic basalt is an important component ofcrust returned to the mantle via plate subduction, so GA2 maybe representative of one of many different mafic lithologiespresent in the upper mantle. During upwelling of heterogeneousmantle domains, these mafic rock-types may undergo extensivemelting at great depths, because of their low solidus temperaturescompared with mantle peridotite. Melt batches may be highlyvariable in composition depending on the composition and degreeof melting of the source, the depth of melting, and the degreeof magma mixing. Some of the eclogite-derived melts may alsoreact with and refertilize surrounding peridotite, which itselfmay partially melt with further upwelling. Such complex magma-genesisconditions may partly explain the wide spectrum of primitivemagma compositions found within oceanic basalt suites. KEY WORDS: eclogite; experimental petrology; mafic magmatism; mantle melting; oceanic basalts  相似文献